The present invention relates to a protected pseudouridine in crystal form (hereinafter referred to as a crystalline protected pseudouridine), which is a useful material for producing an RNA oligomer or a similar substance, and to a method for producing the crystalline protected pseudouridine.
A phosphoroamidite derivative of pseudouridine is employed as a material for the chemical autosynthesis of RNA oligomers including a modified nucleoside. For example, a phosphoroamidite derivative of pseudouridine is used as a starting material in the synthesis of tRNA of yeast (see Biochimie, 77, 125 (1995)).
In recent years, genome-base drug discovery, which employs aptamers, RNA interference, etc., has become of interest, and a phosphoroamidite derivative of pseudouridine is employed as one of the starting materials for synthesizing such oligomers.
The chemical autosyntesis of an RNA oligomer including pseudouridine is usually carried out by employment of a 3′-phosphoroamidite derivative of pseudouridine whose 5′- and 2′-hydroxyl groups are protected with an appropriate protective group. Specifically, the aforementioned document discloses a 3′-(2-cyanoethyl-N,N-diisopropyl)phosphoroamidite derivative of pseudouridine, whose 5′-position is protected with a 4,4′-dimethoxytrityl (DMTr) group and whose 2′-position is protected with a t-butyldimethylsilyl (TBDMS) group.
Such a phosphoroamidite derivative is synthesized through, sequentially, introducing DMTr into the 5′-position of pseudouridine, introducing TBDMS into the 2′-position, and introducing an amidite into the 3′-position. In the first step of introducing DMTr into pseudouridine, 4,4′-dimethoxytrityl chloride (DMTrCl) is reacted with pseudouridine in pyridine at room temperature, followed by phase separation and purification by means of a silica gel column, to thereby recover a protected species of interest. The aforementioned document does not disclose properties of the 5′-DMTr derivative of pseudouridine. However, another document (Helvetica Chimica Acta, 78, 1705 (1995)) discloses that the 5′-DMTr derivative of pseudouridine synthesized in the same procedure assumes the form of colorless foam.    Non-Patent Document 1: Biochimie, 77, 125 (1995)    Non-Patent Document 2: HELVETICA CHIMICA ACTA, 78, 1705 (1995)